1. Field of the Invention
The present invention relates to a capacitive touch panel and a display device with a touch panel having the touch panel mounted thereon.
2. Description of the Related Art
In recent years, a display device with a touch panel, in which a display input device, such as a cellular telephone, a ticket vending machine, or a hand-held game machine, is combined with a touch panel, has widely been put into practical use. In the display device with a touch panel, a button to touch is displayed on the display device. When a portion indicated by the button is pressed by a finger, a pen, or the like, the pressing is detected and corresponding information is input. Based on the input information, image displayed by the display device is switched, and the next input or other kind of operation is carried out. In the display device with a touch panel, a touch sensor is integrally formed on a display screen of the display device, which saves space. Further, the position and function of an input button may be freely changed, which enhances the operability of the device.
FIG. 11 schematically illustrates a structure of a conventional capacitive touch sensor (see, for example, US 2007/0273560 A1). A plurality of black rhombic detection electrodes 503 and a plurality of outline rhombic detection electrodes 501 are formed on a surface of a flat substrate. The black rhombic detection electrodes 503 are connected to row electrodes 504 while the outline rhombic detection electrodes 501 are connected to column electrodes 505. The row electrodes 504 and the column electrodes 505 are connected to a processing device 210 via wiring 502. When a conductive object 303 approaches the surface, capacitances of a row electrode 504 and a column electrode 505 approached by the conductive object are changed. The changes in capacitance are detected by the processing device 210, and the row and column approached by the conductive object 303 are determined. In this way, the position of the conductive object 303 is determined.
In the capacitive touch sensor, the position of a conductive object such as a finger or a pen may be determined even when the conductive object does not touch or only lightly touches the surface of the substrate having sensor elements formed thereon, and hence a high degree of operability is realized. Further, the capacitive touch sensor may be formed using only one substrate, and hence the capacitive touch sensor may be formed thinner and more lightweight as compared with a resistive touch sensor. Further, even when an insulator such as a cover glass is provided on the surface to be touched, input may be carried out from above the insulator, and hence design flexibility may be enhanced.
FIG. 12 is a schematic longitudinal sectional view of an example of a display device 60 with a touch panel, in which a touch panel 63 is provided on a display panel 64. The touch panel 63 is provided on an upper surface of the display panel 64 while a drive circuit 65 is provided on a rear surface side of the display panel 64. A cover glass 61 is provided on an upper surface of the touch panel 63. An edge cover 62 for covering edges of the display is formed on an outer periphery of the cover glass 61. The touch panel 63, the display panel 64, and the drive circuit 65 are housed in a housing 66 made of a conductor.
In a capacitive touch panel, when a conductor approaches a detection electrode, capacitance between the conductor and the detection electrode changes. By detecting weak current caused by the changed capacitance, the position of the conductor is determined. However, a capacitive touch panel has a problem that electromagnetic noise and static electricity which come around from the upper surface of the substrate except for a detection region or from an edge portion of the substrate are input to a detection electrode or a wiring electrode, leading to erroneous determination. For example, as illustrated in FIG. 12, electromagnetic noise Z1 makes an entry through a small gap between the cover glass 61 and the housing 66. Further, an electromagnetic wave generated from the display panel 64 or the drive circuit 65 may also enter as electromagnetic noise Z2 to be applied to a wiring electrode or a detection electrode of the touch panel 63, leading to erroneous determination.